Skin-whitening activity of a tranexamate compound is known, and a tranexamate compound has been used as a skin-whitening ingredient in compositions for external use, such as drugs, quasi-drugs, and cosmetics. For example, Japanese Patent Laid-Open No. 04-46144 discloses an anti-pigmentation agent for external use using a tranexamate compound as an active ingredient. Japanese Patent Laid-Open No. 2003-306419 exemplifies tranexamic acid and derivatives thereof as a skin-whitening ingredient to be usable with Coenzyme Q10. Japanese Patent Laid-Open No. 2004-107262 exemplifies cetyl tranexamate as an oil-soluble skin-whitening ingredient to be usable with an L-ascorbic acid tetra-branched fatty acid ester derivative.
However, a tranexamate compound or a salt thereof is sparingly soluble in water or oil, and so it is likely to cause aggregates in a formulation. Thus, it is difficult to incorporate it in a formulation in a homogeneous state.
Japanese Patent Laid-Open No. 2002-234836 discloses an anti-stress external preparation for skin using a tranexamate as an active ingredient. It also discloses a method to dissolve a tranexamate using a large amount of an oil component such as an olive oil. However, by this method, the formulation form is limited to a cream or a milky lotion due to the use of a large amount of an oil component. Additionally, the obtained external preparation is sticky and oily, and very uncomfortable to use.
Further, Japanese Patent Laid-Open No. 2006-306744 discloses an external preparation for skin using a tranexamate or a salt thereof as well as a silicone oil. The same teaches that by the combination of a tranexamate or a salt thereof and a silicone oil, the solubility of the tranexamate or a salt thereof in the composition can be enhanced, and the activity of the tranexamate can last over an extended time period. Although the silicone oil is known as an oil component which is comfortable to use, due to the necessity to use a large amount of silicone oil to dissolve the tranexamate, the range of choice for the skin external preparations becomes narrow.
In the meantime, Japanese Patent Laid-Open No. 2006-45079 describes that a stable cosmetic material can be obtained by using a whitening ingredient such as sodium tranexamate together with a polymer compound having a quaternary amino group such as polyquaternium. However, all the whitening ingredients described here including sodium tranexamate are water-soluble compounds, and thus the problem of dissolution in a formulation does not occur.
The patent application WO00/57841 describes that a polysaccharide-cholesterol derivative can be utilized as a moisture retention ingredient in a cosmetic material. However, it is not described that an ingredient having a low solubility in water and oil can be dispersed in a formulation by using a polysaccharide-cholesterol derivative.